Title: What can we learn from GRB afterglows? Implications for the central engine and shock acceleration
Abstract: Although almost 50 years have gone by since the first discovery of Gamma Ray Bursts, there is still no physical model able to explain all GRB observations. The afterglow phase that follows the prompt GRB, is much better understood and is well modeled by synchrotron radiation from the forward external shock created as the relativistic jet collides with the external medium. However, broadband modelling attempts of different GRBs often result in large uncertainties and seem to imply wide distributions of the underlying physical parameters. I will present a tool based on detections of radio afterglows to help constrain future modeling. Furthermore, peculiarities such as flares and extended plateaus in X-ray light-curves challenge our understanding of GRB physics. These phenomena can shed new light on the prompt phase and provide important clues on the underlying parameters. In particular they impose large energy requirements and considerably limit the magnetization and Lorentz factor distribution in the flow as well as the size of the emitting region.